1. Field of the Invention
The invention relates to a high-temperature protection layer of an alloy with a base of aluminum, chromium and nickel, adapted particularly for protecting structural gas-turbine elements of an austenitic material.
2. Description of the Prior Art
Such high-temperature protection layers find application particularly in protecting the base material of structural elements of heat resistant steels and/or alloys which are used at temperatures above 600.degree. C. These high-temperature protection layers are to retard the effect of high-temperature corrosion particularly of sulfur, oil ashes, oxygen, earth alkalies and vanadium. The high-temperature protection layers are applied directly to the base material of the structural element. High-temperature protection layers are of particular importance in structural elements of gas turbines. They are applied particularly to rotor and guide vanes as well as to segments of gas turbines subject to localized heat. In manufacturing these structural elements, an austenitic material based on nickel, cobalt or iron is preferably used. In the manufacture of gas-turbine parts, nickel superalloys particularly are used as the base material. The high-temperature protection layers to be applied consist preferably of chromium-containing alloys. It has been customary heretofore to use two high-temperature protection layers, of which one of them is suitable for parts which are subjected to temperatures below or around 900.degree. C. Under operating conditions, where the high-temperature protection layer is stressed thermally, this protection layer develops at its surface a passive cover layer of chromium oxide.
A second high-temperature protection layer is known which is preferably applied to parts which are subjected to the effects of temperature substantially above 900.degree. C. This high-temperature protection layer has the property, when under operating conditions under which it is stressed thermally, of developing a passive cover layer of aluminum oxide on its surface.
A disadvantage of each of these high-temperature protection layers is that each is suitable only for a very definite temperature range. For structural parts which are subjected to changing temperature influences, especially to those in which the temperature range varies between values below 900.degree. C. and far above 900.degree. C., optimum protection is not possible since neither of the two mentioned protection layers is suitable for both operating conditions.